Image scanning devices in which an image on a manuscript is formed on an image pickup device, such as a CCD, via an optical system in order to convey the image information are known. Recently, miniaturization and low cost have been required in such image scanning devices, especially in image scanners and similar devices, in turn making low cost and miniaturization of the image scanning lens highly desirable.
Various types of image scanning lenses used in image scanning devices, such as facsimile machines and image scanners, are known. For example, Japanese Laid-Open Patent Application H09-127414 and Japanese Laid-Open Patent Application H05-264900 disclose such image scanning lenses of four-component, five-element construction that are small and have low production costs.
However, recently, high resolution has become an urgent need in image scanning devices, such as facsimile machines and image scanners, tending to sharply increase the number of pixels needed in the image pickup devices. As the number of pixels is increased, the size of the image pickup element becomes larger, making it difficult to obtain an image scanning lens having desirable image magnification, a wide field of view, and sufficient miniaturization.
Additionally, because high precision has been increasingly required in reading color images, it is strongly desired to make an image scanning lens that can favorably correct aberrations related to color.
However, the half-field angles of the image scanning lenses described in the above mentioned Japanese Laid-Open Patent Application H09-127414 are relatively narrow, 18 to 20 degrees, which does not respond to the need for a wide angle of view. On the other hand, the half-field angles of the image scanning lenses described in Japanese Laid-Open Patent Application H05-264900 are relatively wide at about 23.5 degrees, but they are not necessarily sufficient in terms of the correction of lateral color to enable desired reading of color images.